A FE analysis on reliability of thick aluminum wire with different pad structures in power module

In power modules, thick Al wires are usually bonded to the chip pad by ultrasonic bonding to realize the electrical interconnection. And the root shedding of the wire under the action of cyclic thermal stress is one of the main failure modes of power modules. Therefore, the related research on the pad is of great significance to improve the reliability of the thick Al wire. In this work, three typical pad structures are selected, including commonly used Al pad, thick Cu pad and Cu/Al composite thick pad. The power cycling (PC) and temperature cycling (TC) simulations were carried out on samples with three pad structures by using the finite element (FE) method. The influence of using different pad structures on the lifetime of thick Al wire is discussed from these two ways. The results show that thick pads can act as a buffer layer between the chip and the wires. Thick pad improves the reliability of thick Al wire. And the sample with thick Cu pads have the longest lifetime under TC, while the sample with Cu/Al composite thick pads have the longest lifetime under PC.